Does the longer application of anodal-transcranial direct current stimulation increase corticomotor excitability further? A pilot study

Introduction: Anodal transcranial direct current stimulation (a-tDCS) of the primary motor cortex (M1) has been shown to be effective in increasing corticomotor excitability. Methods: We investigated whether longer applications of a-tDCS coincide with greater increases in corticomotor excitability compared to shorter application of a-tDCS. Ten right-handed healthy participants received one session of a-tDCS (1mA current) with shorter (10 min) and longer (10+10 min) stimulation durations applied to the left M1 of extensor carpi radialis muscle (ECR). Corticomotor excitability following application of a-tDCS was assessed at rest with transcranial magnetic stimulation (TMS) elicited motor evoked potentials (MEP) and compared with baseline data for each participant. Results: MEP amplitudes were increased following 10 min of a-tDCS by 67% (p=0.001) with a further increase (32%) after the second 10 min of a-tDCS (p=0.005). MEP amplitudes remained elevated at 15 min post stimulation compared to baseline values by 65% (p=0.02). Discussion: The results demonstrate that longer application of a-tDCS within the recommended safety limits, increases corticomotor excitability with after effects of up to 15 minutes post stimulation.